<table>
  <tr>
    <th>Parameter</th>
    <th>Type</th>
    <th>Description</th>
  </tr>
  <tr>
    <td><code>lookup</code></td>
    <td>An object</td>
    <td>An object specifying the key (copied from a request field), the data source,
    and the response token</td>
  </tr>
  <tr>
    <td><code>lookup.key</code></td>
    <td>An object</td>
    <td>The information on how to select the key from the request.</td>
  </tr>
  <tr>
    <td><code>lookup.key.from</code></td>
    <td>A string or an object</td>
    <td>The name of the request field to select from, or, if the request field is an object,
    then an object specifying the path to the request field. For example,
    <pre><code>{ "from": "body" }</code></pre> and <pre><code>{ "from": { "query": "q" } }</code></pre>
    are both valid.</td>
  </tr>
  <tr>
    <td><code>lookup.key.using</code></td>
    <td>An object</td>
    <td>The configuration needed to select the key from the response</td>
  </tr>
  <tr>
    <td><code>lookup.key.using.method</code></td>
    <td>A string</td>
    <td>The method used to select the key from the request. Allowed values are <code>regex</code>,
    <code>xpath</code>, and <code>jsonpath</code>.</td>
  </tr>
  <tr>
    <td><code>lookup.key.using.selector</code></td>
    <td>A string</td>
    <td>The selector used to select the key from the request. For a <code>regex</code>, this would
    be the pattern, and the replacement value will be the entire match by default.
    <code>xpath</code> and <code>jsonpath</code> selectors work on XML and JSON documents. If the request
    value does not match the selector (including through XML or JSON parsing errors), nothing is replaced.</td>
  </tr>
  <tr>
    <td><code>lookup.key.using.ns</code></td>
    <td>An object</td>
    <td>For <code>xpath</code> selectors, the <code>ns</code> object maps namespace aliases to URLs</td>
  </tr>
  <tr>
    <td><code>lookup.key.using.options</code></td>
    <td>An object</td>
    <td>For <code>regex</code> selectors, the <code>options</code> object describes the regular expression options</td>
  </tr>
  <tr>
    <td><code>lookup.key.using.options.ignoreCase</code></td>
    <td>A boolean</td>
    <td>Uses a <a href='https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/RegExp/ignoreCase'>case-insensitive</a>
    regular expression</td>
  </tr>
  <tr>
    <td><code>lookup.key.using.options.multiline</code></td>
    <td>A boolean</td>
    <td>Uses a <a href='https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/RegExp/multiline'>multiline</a>
    regular expression</td>
  </tr>
  <tr>
    <td><code>lookup.key.index</code></td>
    <td>An int (defaults to 0)</td>
    <td>Each of the selection options returns an array: <code>regex</code> returns an array of parenthesized
    gropus (with the entire match in the 0th index), and <code>jsonpath</code> and <code>xpath</code>
    return an array of matches. This field selects the appropriate value from the array to use as
    the lookup key into the data source.</td>
  </tr>
  <tr>
    <td><code>lookup.fromDataSource</code></td>
    <td>An object</td>
    <td>Configuration for the external data source to lookup data based on the key. Each
    <code>lookup</code> configuration may only specify one data source.</td>
  </tr>
  <tr>
    <td><code>lookup.fromDataSource.csv</code></td>
    <td>An object</td>
    <td>Configuration for using a CSV file as the data source</td>
  </tr>
  <tr>
    <td><code>lookup.fromDataSource.csv.path</code></td>
    <td>A string</td>
    <td>The path to the CSV file, which must be readable by the <code>mb</code> process</td>
  </tr>
  <tr>
    <td><code>lookup.fromDataSource.csv.keyColumn</code></td>
    <td>A string</td>
    <td>The header of the column to scan for a match against the key. If a match is
    found, the entire row will be returned.</td>
  </tr>
  <tr>
    <td><code>lookup.fromDataSource.csv.delimiter</code></td>
    <td>A string(default to comma ,)</td>
    <td>The delimiter separated colums in CSV file.</td>
  </tr>
  <tr>
    <td><code>lookup.into</code></td>
    <td>A string</td>
    <td>The token to replace in the response with the selected request value. There is
    no need to specify which field in the response the token will be in; all response
    tokens will be replaced in all response fields. A successful match will return a
    hashmap or dictionary type object, with named indexes. For example, if you specify
    <pre><code>{ "into": "${NAME}" }</code></pre> as your token configuration, and the
    data source returned a row containing "first" and "last" fields, then
    <code>${NAME}["first"]</code> and <code>${NAME}["last"]</code> will be replaced by
    the appropriate data. You can quote the field name with double quotes, single quotes,
    or no quotes at all.</td>
  </tr>
</table>

<p>The <code>lookup</code> behavior supports dynamically replacing values in the response with something that
comes from an external data source. Looking up the values from the data source requires first selecting
the key value from the request. The key selection and replacement behavior in the response mirrors the
functionality for the <code>copy</code> behavior. We'll look at the following examples:</p>

<ul class='bullet-list'>
  <li><a href='#lookup-regex-replacement'>Lookup up from a CSV file based on a key selected with a regular expression</a></li>
</ul>

<p class='info-icon'>Look at the <code>copy</code> examples to see how to do advanced key
selection using jsonpath and xpath.</p>

<testScenario name='lookup'>

<p>We'll use the following CSV file for these examples, saved as "values.csv" in the
current working directory of the <code>mb</code> process (you can always use an absolute path):</p>

    <step type='file' filename='<%= process.cwd() %>/values.csv'>
<pre><code>State_ID,code,Name,price,tree,jobs
1111111,400,liquid,235651,mango,farmer
9856543,404,solid,54564564,orange,miner
2222222,500,water,12564,pine,shepherd
1234564,200,plasma,2656,guava,lumberjack
9999999,200,lovers,9999,dogwood,steel worker</code></pre>
    </step>

<h3 id='lookup-regex-replacement'>Lookup up from a CSV file based on a key selected with a regular expression</h3>

<p>The following example shows selecting the key using a regular expression to match against the path. We're
using the <code>index</code> field to select the first parenthesized group in the regular expression.</p>

    <step type='http'>
<pre><code>POST /imposters HTTP/1.1
Host: localhost:<%= port %>
Accept: application/json
Content-Type: application/json

{
  "port": 9595,
  "protocol": "http",
  "stubs": [
    {
      "responses": [
        {
          "is": {
            "statusCode": "<strong class='highlight1'>${row}['code']</strong>",
            "headers": {
              "X-Tree": "<strong class='highlight1'>${row}['tree']</strong>"
            },
            "body": "Hello <strong class='highlight1'>${row}['Name']</strong>, have you done your <strong class='highlight1'>${row}['jobs']</strong> today?"
          },
          "behaviors": [
            {
              "lookup": {
                "key": <strong class='highlight2'>{
                  "from": "path",
                  "using": { "method": "regex", "selector": "/(.*)$" },
                  "index": 1
                }</strong>,
                "fromDataSource": {
                  "csv": {
                    "path": "<%= process.cwd() %>/values.csv",
                    "keyColumn": "Name",
                    "delimiter": ","
                  }
                },
                "into": "<strong class='highlight1'>${row}</strong>"
              }
            }
          ]
        }
      ]
    }
  ]
}</code></pre>
    </step>

<p>As with the <code>copy</code> behavior, we can plug tokens into any of the response fields
(including the <code>statusCode</code>). Let's see what happens when we craft a request to match
all of those selectors:</p>

    <step type='http'>
<pre><code>GET /<strong class='highlight2'>liquid</strong> HTTP/1.1
Host: localhost:9595</code></pre>

        <assertResponse>
<pre><code>HTTP/1.1 <strong class='highlight1'>400</strong> Bad Request
X-Tree: <strong class='highlight1'>mango</strong>
Connection: close
Date: <volatile>Thu, 28 Dec 2016 11:37:31 GMT</volatile>
Transfer-Encoding: chunked

Hello <strong class='highlight1'>liquid</strong>, have you done your <strong class='highlight1'>farmer</strong> today?</code></pre>
        </assertResponse>
    </step>

    <step type='http'>
<code class='hidden'>DELETE /imposters/9595 HTTP/1.1
Host: localhost:<%= port %></code>
    </step>

    <step type='file' filename='<%= process.cwd() %>/values.csv' delete='true'><code>
    </code></step>
</testScenario>
